The present invention relates to a cordless telephone system and, more particularly, to a hold control system in a cordless telephone system having a hold function.
As shown in FIG. 1, a conventional cordless telephone system having a hold function comprises a plurality of radio telephone sets 1 having an identical arrangement, a connection apparatus or connector 2 coupled to the radio telephone sets 1 via a radio channel 3, and a subscriber telephone set 5 connected to the connector 2 through a subscriber line 4 and a telephone exchanger 6.
Each radio telephone set 1 includes dial keys, a talk button, a talk completion button, and a hold button. The connector 2 includes a talk/hold switch for switching between the talk mode and the hold mode, and a controller for controlling the operation of the talk/hold switch.
FIG. 2 is a sequence diagram for explaining the hold control operation of the cordless telephone system having a hold function.
Referring to FIG. 2, vertical lines A, B, C, D, and E represent a person or bearer using the radio telephone set 1, the radio telephone set 1, the controller in the connector 2, the talk/hold switch in the connector 2, and the subscriber telephone set 5 and its bearer, respectively. The operation sequence progresses downward in FIG. 2. Continuation of arrows represents a chain of operations of portions A to E which are caused by one operation by the radio telephone set bearer A.
When a communication channel is being established and talking is performed between the radio telephone set 1 and the subscriber telephone set 5 in an operation sequence and the radio telephone set bearer A depresses the hold button in the radio telephone set 1 in a sequence b, a radio hold signal is transmitted from the radio telephone set 1 to the connector 2. The controller in the connector 2 sends the hold signal to the talk/hold switch to set it in the hold position. At the same time, holding tone or music is sent to the subscriber telephone set 5. The communication channel is then held in the hold state. When the radio telephone set bearer A on-hooks the radio telephone set 1 in an operation sequence c, the radio telephone set 1 outputs the hold signal to cause the controller in the connector 2 to generate and send the holding music to the subscriber telephone set 5. When the radio telephone set bearer A off-hooks the radio telephone set 1 in an operation sequence d, the radio telephone set 1 stops sending the hold signal. In this case, the transmitter in the radio telephone set 1 transmits only a radio carrier signal. The controller in the connector 2 sets the talk/hold switch in the talk position and stops sending the holding music. As a result, the hold state of the communication channel is set in the busy state in a sequence e.
In the conventional hold control system described above, the radio channel is maintained even during the hold period. However, since talking is not performed in the hold period, the radio channel need not be maintained. This mode of operation is not preferable from the viewpoint of effective utilization of radio or electric waves.
In a system having a plurality of radio telephone sets 1, a demand has arisen to allow an operation wherein the communication channel held in the hold state by one radio telephone set, e.g., 1-(1) can be released by another radio telephone set, e.g., 1-(2) to restart talking. However, the demand cannot be satisfied.